Radiation-sensing and control apparatus



June 6, 1967 .1. T. Ivi-:s

RADIATIONSENSING` AND CONTROL APPARATUS Filed April 24, 1963 5 Sheets-Sheet l June 6, 1967 J. T. NES 3,324,274

RADIATION-SENSING AND CONTROL APPARATUS Filed April 24, 1963 5 Sheets-Sheet g June 6, 1967 J. T. lVEs RADIATION-SENSING AND CONTROL APPARATUS Filed April 24, 1965 5 Sheets-Sheet 3 United States Patent O M 3,324,274 RADIATION-SENSING AND CONTROL APPARATUS John 'I'. Ives, Pennington, NJ., assigner to Western Electrie Company Incorporated, New York, N.Y., a corporation of New7 York Filed Apr. 24, 1963, Ser. No. 275,332

22 Claims. (Cl. 219-50) The present invention relates to radiation-sensing and control apparatus and more particularly, -but not exclusively, 'to radiation-sensing devices utilizing a combined turbine-wheel and radiation-chopping element.

In the manufacture of transistors, it is frequently necessary to bond a wafer of semieonductive material (i.e., silicon) to a gold-plated transistor header by means of a gold-silicon eutectic bond. This is accomplished in some cases by resistance heating of the header to form the eutectic bond. Because of the very temperature-sensitive nature of the semiconductive material, such heating must lbe controlled precisely to hold the temperature of the header at approximately 370 C., which is the melting point 4of the gold-silicon .eutect-ic.

An object of the' present invention is to provide new and improved radiation-sensing and control apparatus.

Another objeot of the present invention is to provide new and improved radiation-chopping devices utilizing combined turbine-wheel and radiation-chopping elements.

A further object of the `present invention is to provide new and improved temperature-monitoring devices employing combined turbine-wheel and radiation-chopping elements for use in heat-control systems.

A still further object of the present invention is to provide new and improved current-variable resistance circuits particularly adaptable for use in phase Shifters for heat-control systems. y

A radiation-chopper embodying certain principles of the present invention may include means for directing a beam of radiation along a predetermined path, A unitary, rotatable `turbine-wheel and radiation-chopping element, having a plural-ity of turbine blades formed thereon and at least one radiation-transmitting aperture therein, is arranged so that the aperture in the element moves periodically across the beam of radiation during rotation of the element. Means are provided for directing a fluid medium against the turbine blades to rotate the element to cause periodic transmission of the lbeam of radiation through the aperture in the element.

Other objects and features of the present invention may be more readily understoodA from `the following detailed description of specific embodiments thereof when read in conjunction with the accompanying drawings in which:

FIG. l is a block diagram of a heat-control system, including exemplary embodiment of a radiation-sensing device with portions of the latter broken away to illustrate details of a combined turbine-wheel and radiationchopping element; y

FIG. 2 is an enlarged, horizontal, sectional view of the radiation-sensing device of FIG. 1 taken along. line 2 2 thereof;

FIG. 3 is an enlarged, horizontal, sectional View of the radiation-sensing device of FIG. l taken along line 3 3 thereof;

FIG. 4 is an enlarged, irregular, vertical, sectional View of the radiation-sensing device of FIG. 3 taken along' line 4 4 Ithereof with the clearance between the combined turbine-wheel and radiation-chopping element and the housing of the device being exaggerated for clarity; and

FIG. 5 is a schematic diagram of an electrical control circuit for the heat-control system illustrated on FIG. 1.

Referring now to the drawings and more particularly to FIGS. 1 and 5 thereof, there is shown a heat-control 3,324,274 Patented June 6, 1967 system, designated generally by the numeral 10, for detecting and precisely controlling the temperature of a gold-plated transistor header 11 (FIG. 1) in the area of a bond being formed between a wafer 12 of a semiconductive material and the header 11 during a waferbonding operation. The system 10 provides a closed loop system to bring the header 11 rapidly up to a predetermined temperature and to hold that temperature precisely. The transistor header 11 is mounted in a suitable holding fixture (not shown) where it is engaged on opposite edges by contacts 13 13 of a resistance-heating circuit, designated generally lby the numeral 16. Current is supplied to the resistance-heating circuit 16 through a transformer, designated generally by the numeral 17, from a power supply, designated generally by the numeral 18, including a silicon-controlled-rectiiier unit, designated generally by the numeral 21.

The silicon-controlled-rectiiier unit 21 contains two silicon-controlled rectiers 22-22 (FIG. 5) which function like solid-state thyratrons. The silicon-controlled rec- .,t-iiiers 22 22 prevent current from flowing until one of 'the rectiiiers 2Z 22 is triggered, at which time the triggered rectifier 22 conducts heavily and contlnues to conduct until its anode voltage is reversed or until its forward current drops below a fixed holding current. ,The silicon-controlled rectiiiers 22-22 are controlled by phase-shifted, trigger pulses from a pulser unit, designated generally by the numeral 23, including a unijunction transistor 26. The phase angle -of the trigger pulse relative to the anode voltage impressed on the silicon-controlled recti'iers 22 22 is controlled by a transistorized phase v shifter, designated generally by the numeral 27. The output of the phase shifter 27 is a 60-cycle, sine wave, the phase angle of which is shifted in response to changes in the magnitude and polarity of an error s-ignal produced by an infrared heat or radiation sensor, designated generally by the numeral 31, which is indicative of a difference between observed radiation from the heated transistor header 11 and an adjustable standard -sou-rce of radiation 32 (FIG. 3).

The radiation sensor 31 includes a cylindrical, metal body portion 36 which is split into two parts 37 and 38.

The pa-rts 37 and 38 are machined to provide an opaquehousing, designated generally by the numeral 39, for various components of the sensor. A metal sleeve 41, open on both ends and threaded internally on one end thereof,

ts over the body port-ion 36 and is fastened thereto by external threads 42 on one end of the split body portion 36 to hold the :two parts 37 and 3S of the lbody portion 36 together. The one part 37 of the body portion 36 is provided with a turbine cavity 43 designed to receive one end of a closely fitting, substantially cylindrical, combined turbine-wheel and radiation-chopping element, designated generally by the numeral 46, for rotation, about a shaft 47 extending through a central aperture 48 in the element, on a pair of ball bearings 51 51 (FIG. 4).

The shaft 47 is formed integrally with and extends upwardly from the bottom of the turbine lcavity 43 formed in the part 37 of the body portion 36 and extends into a relatively shallow bore 49 formed in the center of a similar, cooperating, turbine cavity 52 provided in the other part 38 of the body portion 36. An annular shoulder 53 is provided in each of the cavities 43 and 52 in the parts 37 v and 38 respectively, of the body portion 36 around opposite ends of the shaft 47 when the body portion 36 is Y assembled. The inner races of the ball bearings 51-51, mounted in counterbores 54 54 in the combined turbinewheel 'and radiation-chopping element 46, rest against the annular shoulders 53 53. A spring-loaded washer (not shown) is provided between one of the shoulders 5? 53 and one of the bearings 51 51 to preload the bearings.

The end surfaces of the combined turbine-wheel and radiation-chopping element 46 are slotted to provide a plurality of nadially extending fins 56-56 on the periphery of the element which serves as turbine blades. The turbine blades 56-56 are formed symmetrically with respect to a rounded inte-rsection between each end and the sides of the cylindrical element 46 by cutting equallyspaced arcuate slot-s 57-57 radially of the element in each end thereof.

The -combined turbine-wheel and radiation-chopping element 46 is provided winh six identically shaped, rectangular apertures 58-58 spaced around the outer periphery of the element 46 at equally spaced intervals. Material has been removed from the central portion of the element 46 by passing a milling tool chordally through the element between alternate apertures 58--58. The only portion of the cylindrical element 46 remaining between parallel planes containing the tops 61-61 and bottoms 62-62 of the apertures 58-58 after the milling operation is completed are thin Webs 63-63, of substantially triangular cross section, on the periphery of the element 46 extending between adjacent apertures 58-58. The webs 63-63 are the same length as the length of the apertures 58-58 so that the spacing between adjacent ends 64-64 of the apertures is equivalent to the length of the apertures.

Air inlet 66-66 are provided to direct air under pressure, from flow-rate valves 68-68, tangentially of the rounded intersecting portion of the element 46 against the fins 56-56 to drive the combined turbine-wheel and radiation-chopping element 46 in a clockwise direction, as viewed in FIGS. 2 and 3. Exhaust outlets 71-71 are provided to remove the streams of pressurized air from the cavities 43 and 52. The stream of pressurized air, normally directed against the fins 56-56 on either or both ends of the element 46, may be shut off by closing the associated flow-rate valves 68-68. There is considerable advantage in driving the radiation-chopping element by a fluid medium instead of by conventional electric drive motors. By using pressurized air to drive the radiationchopping element, electrical interferences and heat generated inherently by electrical drive motors, which would aiiect the sensitivity of various circuit elements in the sensor 31, are eliminated. Instead of generating heat, the streams of pressurized air used to drive the combined turbine-wheel and radiation-chopping element 46 will provide a heat transfer medium which will stabilize the temperature of the sensor 31 and prevent the temperature of the sensor from increasing as a result of the standard radiation and the observed radiation. The combined turbine-wheel and radiation-chopping element 46 is simple-r to construct, requires fewer moving parts, is more dependable and requires less maintenance than conventional light-chopping devices.

The radiation sensor 31 includes a sapphire rod 76 which is designated to transmit infrared radiation from the resistance-heated transistor header 11 to the interior of the sensor 31. The rod '76, by virtue of total internal reflection, directs the infrared image toward a radiationsensitive cell 77, for example, a Kodak Ektron leadsulphide detector, mounted in a cut-out portion on one side of the shaft 47 about which the substantially cylindrical chopper element 46 is designed to rotate. The heated header 11 gives off infrared radiation as a function of its temperature, area and emissivity. This radiation is given off over a wide range of wavelengths but has a peak emission which increases in amplitude and decreases in Wavelength as its temperature increases. Since the cell 77 is sensitive to the total radiation, over its response range, it will measure a product of area, emissivity and temperature. The area of observation is held constant by utilizing a 0.050-inch Adiameter sapphire rod 76. Interference from room lighting and other stray visible radiation is eliminated by providing a iilter 7-8 which is used to cut out 4 radiation having wavelengths sho-rter than approximately 0.7 micron.

As the turbine-wheel and radiation-chopping element 46 rotates, infrared radiation from the heated transistor header 11 is transmitted via the sapphire rod 76, through the filter 78, and strikes the cell 77 intermittently at a rate determined by the speed of rotation of the combined turbine-wheel and radiation-chopping element 46. It may be seen that the observed radiation from the transistor header 11 is modulated by the element 46 and will strike the cell 77 only during the time that one of the apertures 58-58 uncovers the end of the rod 76.

The cell 77 is also illuminated intermittently by radiation from the preset standard reference lamp 32. The standard radiation from the lamp 32 is directed toward the cell 77 throughra path oriented at an angle with respect to the path of travel of the observed radiation from the header 11 toward the cell 77. rI'he distance between the points where the paths of the standard radiation and the observed radiation cross the path of travel of the apertured portions of the element 46 is equivalent to the distance between adjacent edges 64-64 of the apertures 48-48. In this way the standard radiation passes to the cell 77 whenever one of the apertures 58-58 uncovers the latter.

The amount of radiation from the reference lamp 32 may tbe changed by changing the size of apertures 82-82 of a double-pinhold, collimator stop 81. This allows the reference lamp 32 to be burned at approximately half brilliance for the particular operating temperature and thus increase the stable life of the lamp. The power input to the lamp 32 can also be adjusted to vary the standard radiation. It should be noted that the stop apertures 82- 8-2 are closed by the element 46 whenever the sapphire rod 76 is uncovered by one of the apertures 58--5'8 in the element 46 and vice versa. Thus, the cell 77 alternately receives olblserved radiation from the transistor header 11 and standard radiation from the reference lamp 32, respectively.

The output signal of the cell 77 is substantially a square Wave, the difference between the maxima and minima of which represents the error between the observed radiation and the standard radiation. By making the outuut signal representative of the Idierence between the observed radiation and the preset reference radiation, instead of providing independent output signals from separate cells indicative of the actual amounts of the two different types of radiation impinging alternately on the .cell 7'7, the absolute response of the signal generating cell 77 is not as critical. Since the output of the cell 77 represents the difference between the amount of the observed and the standard radiation impinging on the cell 77, the stability of the signal generating element (cell 77) which varies with ambient temperature and humidity, is not nearly as critical as if separate signals were generated by the radiant energy from the two separate sources impinging on separate cells.

The output signal of the cell 77 is connected to an A.C. coupled amplifier, desi-gnated generally by the numeral (FIG. 5). A transistor 84 formi-ng a preamplifier or first stage of the amplifier 85 is contained in the housing 39 to shield the preamplifier and reduce the lengths'fof relatively high-impedance leads over which the unamplified signal passes. Since a `single output signal is generated by the observed radiation and the standard radiation, the gain accuracy of the amplifier `85 is not important except for overall loop accuracy and response.

Although an attempt is made -to keep the speed of the combined turbine-wheel and chopper element 46 fairly constant |by adjusting the external, flow-rate valve 68-68, obviously, there may be slight variations in the rotational speed of the element 46. Accordingly, a synchronizing pulse is provided by the output of a light-sensitive cell 86, for example, a Kodak Ektron7 lead-sulphide detector mounted on the shaft 47. The cell 86 and a lamp 87,

aaa/1,274

supplying' synchronizing radiation, are so arranged that the path of the synchronizing radiation from the source 87 to the cell 86 intersects the path of travel of the apertured portion of the element 46, an arcuate distance measured around the periphery of the element from the point of intersection of the path of the observed radiation with the path of travel of the apertured portion of the element equivalent to a multiple of the length of the apertures 58-58. The cell 86 is illuminated by the light source S7 whenever one of the apertures 58-58 uncovers a stop aperture 88. This is made to occur sirnultaneously withe the impingement of the observed radiation on the -cell'77, but could be synchronized with the impingernent of the standard radiation on the cell 77. The synchronizing signal is amplified by a multistage transistor amplifier, designated generally by the numeral 91 (FIGS. 1 and 5) to a square wave for proper gating and easy filtering and is applied to a synchronous demodulator, designated generally b-y the numeral 92. A transistor 89 forming a preamplifier or first stage of the amplifier 91 is contained in the housingV 39 to shield the preamplifier and reduce the lengths of relatively highimpedance leads over which the unamplified signal passes.

The A.C. error signal from the radiation sensor 31 is coupled through the A.C. coupled ampliiier 85 where it is amplified linearly and is applied to the synchronous demodulator 92 to compare the phase of the error signal with the phase of the synchronizing signal produced by the cell 36 to determine if the observed radiation is greater or smaller than the standard radiation. The demodulator 92 has a complementary pair of transistors 97-97 connected so that the synchronizing signal is applied to the collectors 98-98 of the transistors from a center-tapped secondary 100I of a transformer, designated generally by the numeral 99, and the A.C. error signal from the cell 77 is applied to the bases 101-101 of the transistors 97-97.

The particular transistor 97, in the demodulator 92, in which the base input resulting from the error signal and collector input resulting from the synchronizing signal are in phase at a particular time will conduct, and a rectified output from the transistor 97, conducting at any particular instant, is applied to a capacitor 102 connected to the center tap 103 of the transformer 99. A bias 105 is applied to the demodulator 92 which produces an output at the silicon-controlled-rectier unit 21 for zeroerror input at the demodulator. The amount of the bias 105 applied to the demodulator 92 is that required to provide enough power output at the silicon-controlled-rectifier unit 21 to maintain the temperature of the header 11 at approximately 370 C. with a zero error signal. This allows the heat-control system to work around zeroerror voltage with maximum allowance for error in either direction.

Using the proper bias 105, the output of the demodulator 92 is a positive D.C. signalwhich varies in amplitude, depending on the direction and magnitude of the error between the observed radiation and the standard radiation. The D.C. output of the demodulator 92 is utilized to control the phase shifter 27. A 60l-cycle A.C. supply voltage, fed to the phase shifter 27 from a transformer, designated generally by the numeral 107, is shifted in phase Iby a complementary pair of transistors 10S-168 of oppositely conductive types and a capacitor .111 connected across the center-tapped secondary Winding 112 of the transformer 107. The complementary pair of transistors 10B-10S are used so that a given base current, owin-g through both bases 113-113 of the transistors 10S- 108, will cause equal current flow through their collectors 114-114. Diodes 11S-115v isolating the collectors 114-114 guide the collector-current llow during alternate positive and negative half cycles of the alternating `current Wave to charge and discharge the capacitor 11. Equal current flow through the two transistors 108- 108 assures that no D.C. charge is left on the capacitor 6 111. The variation of current flow'thr'ough the transistors 10S-1418 as a function of the bas-e current in effect varies the conductance of the transistors 10S-108i, thereby varying the phase angle of the output between the center tap 116 of the transformer 107 .and a junction 119 of the capacitor 111 and the emitters 117-117 of the transistors 108-108. This phase-shifter 27 requires approximately 80 microamperes base current to control the phase from approximately 12 to 160 which represents power control of the SCRs 22-22 from l/2% to 99% full power.

A unijunction transistor 26 of the pulser 23 provides a pulse through a pulse transformer, designated generally by the numeral 122, for triggering the gates 12S-123 of the SCR unit 21. The trigger pulse is, in turn, gated by a 120-pulse per second spike which provides a trigger to each SCR 22 as its anode 124 becomes positive. This spike is the result of a clipped, full-wave-rectified, 60- cycle, sine wave which is phase shifted with respect to the anode voltage of the SCR 22 to provide one pulse for each half cycle of the 60-cycle wave making 120 pulses per second. The emitter circuit of the unijunction transistor 26 has a relatively short time constant which allows an emitter storage capacitor 125 to be charged and' then discharged through the pulse transformer 122 only once during each of the gate spikes. This keeps the dissipation of the unijunction transistor 26 and the SCR gates 123- 123 to a minimum. The silicon-controlled rectifiers 22-22 are in this way controlled so that they apply the necessary power through a transformer 17 to the contacts 13-13 of the resistance heating circuit 16 to heat the header 11 to the desired temperature and to maintain the header at the desired temperature during the performance of the wafer-bonding operation.

` It is to be understood that the above-described arrangements are simply illustrative of the principles of the invention. Other arrangements may be devised by those skilled in the art which Will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. A radiation chopper which comprises:

means for directing a beam of radiation along a predetermined path;

a unitary rotatable element having a pluralityof turbine blades formed thereon and provided with at least one radiation-transmitting aperture, the aperture being arranged for movement periodically across the beam of radiation during rotation of the element; and

means for directing a fluid medium against the turbine blades to rotate the element to cause periodic transmission of the beam of radiation through the aperture in the element.

2. A radiation chopper, which comprises:

a rotatable element having a plurality of turbine blades formed thereon and having a plurality of radiationtransmitting apertures formed therein,

` a radiation-sensitive cell positioned on one side of the path of travel of successive radiation-transmitting apertures in the element during rotation thereof, means for directing radiation across the path of travel of successive radiation-transmitting apertures in the element toward the radiation-sensitive cell, and means for directingy a iluid medium against the turbine blades of the element to rotate the element and causing successive apertures in the element to cross the path of the radiation being directed toward the radiation-sensitive cell to cause periodic transmission of the radiation to `the radiation-sensitive cell. 3. A radiation-sensing device which comprises:

a rotatable element having a plurality of turbine blades formed thereon and having a plurality of radiationtransmitting apertures formed therein,

a radiation-sensitive -cell positioned on one side of the path of travel of successive radiation-transmitting apertures in the element during rotation thereof,

a source of standard radiation directed toward the radiation-sensitive cell through the path of travel of successive apertures in the element,

means for directing observed radiation toward the radiation-sensitive cell through the path of travel of successive apertures in the element,

the paths of the standard radiation and the observed radiation to the radiation-sensitive cell being disposed Vangularly with respect to each other and intersecting the path of travel of successive apertures in the element at points separated a predetermined distance from each other, and

means for directing a fluid medium against the turbine blades on the element to rotate the element and cause successive apertures in the element to cross the paths of the radiation being directed toward the radiationsensitive cell to cause the radiation from the standard source and observed source to impinge on the cell alternately to generate a signal indicative of the difference in the amounts of observed radiation and standard radiation irnpinging on the cell.

4. A radiation-sensing device, which comprises:

a rotatable element having a plurality of turbine blades formed thereon and having a plurality of radiationtransmitting apertures formed therein;

a. radiation-sensitive cell positioned on one side of the path of travel of successive radiation-transmitting apertures in the element during rotation thereof;

a source of standard radiation directed toward the radiation-sensitive cell through the path of travel of successive apertures in the element;

means for directing observed radiation toward the radiation-sensitive cell through the path of travel of successive apertures in the element;

the paths of the standard radiation and the observed radiation to the radiation-sensitive cell being disposed angularly with respect to each other and intersecting the path of travel of successive apertures in the element at points separated a predetermined distance from each other, the distance between the points of intersection of the paths of the radiation with the path of travel of the successive apertures in the element being equivalent to the distance between the adjacent sides of adjacent apertures; and

means for directing a uid medium against the turbine blades on the element to rotate the element and cause successive apertures in the element to cross the paths of the radiation being directed toward the radiationsensitive cell to cause the radiation from the standard source and observed source to impinge on the cell alternately to generate a signal indicative of the difference in the amounts of observed radiation and standard radiation irnpinging on the cell.

5. A radiation-sensing device, which comprises:

`a rotatable element having a plurality of turbine blades formed thereon and having a plurality of radiationtransmitting apertures of equal size formed therein;

a radiation-sensitive cell positioned on one side of the path of travel of successive radiation-transmitting apertures in the element during rotation thereof;

a source of standard radiation directed toward the radiation-sensitive cell through the path of travel of successive apertures in the element;

means for directing observed radiation toward the radiation-sensitive cell through the path of travel of successive apertures in the element;

the paths of the standard radiation and the observed radiation to the radiation-sensitive cell being disposed angularly with respect to each other and intersecting the path of travel of successive apertures in the element at points separated a predetermined distance from each other, the distance between the Points of intersection of the paths of the radiation with the path of travel of the successive apertures in the element being equivalent to the distance between the adjacent sides of adjacent apertures and the length of the apertures; and

means for directing a uid medium against the turbine blades on the element to rotate the element and cause successive apertures in the element to cross the paths of the radiation being directed toward the radiation-sensitive cell to cause the radiation from the standard source and observed source to impinge on the cell alternately to generate a signal indicative of the diiference in the amounts of observed radiation and standard radiation irnpinging on the cell.

6. A radiation-sensing device, which comprises:

a housing;

a fluid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the peripheray thereof;

a radiation-sensitive cell mounted within the element;

means for directing observed radiation into the interior of the housing toward the radiation-sensitive cell;

a series of circumferential radiation-transmitting apertures of a predetermined size formed in the element at equally spaced intervals; and

means for directing a fluid medium through the housing tangentially of the element against the turbine blades for causing the apertures in the element to cross the path of the observed radiation traveling from its source to the radiation-sensitive cell successively to permit the observed radiation to impinge sequentially upon the radiation-sensitive cell to generate a signal indicative of the intensity of the observed radiation.

7. A radiation-sensing device, which comprises:

a housing; Y

a fluid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the periphery thereof;

a radiation-sensitive cell mounted within the element; means for directing observed radiation into the interior of thehousing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element and being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a series of circumferential radiation-transmitting apertures of a predetermined size formed in the element at equally spaced intervals; and

means for directing a uid medium through the houslng, tangentially of the element and against the turbine blades for causing the apertures in the element to cross the paths of observed and standard radiation traveling from their sources to the radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the radiation-sensitive cell to generate a signal 1nd1cative of the ditference between the amounts of oblslerved radiation and standard radiation striking the ce 8. A radiation-sensing device, which comprises:

a housing;

a fluid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the periphery thereof, a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the side of the element at equally spaced intervals;

a first radiation-sensitive cell mounted within the houslng;

means for directing observed radiation into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a second radiation-sensitive cell mounted within the housing;l

a synchronizing source of radiation being directed tward the second radiation-sensitive cell; and

means for directing a fluid medium through the housing tangentially of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed and standard radiation traveling from their sources to the first radiationsensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the first radiation-sensitive cell to generate a signal indicative of the difference between the amounts of the observed radiation and standard radiation impinging on the first cell and for causing one of the apertures in the element to cross the path of the radiation from the synchronizing source of radiation to the 4Second cell simultaneously with the impingement of radiation from one of the other sources of radiation on the first cell to generate a synchronizing signal.

9. A radiation-sensing device, which comprises:

a housing;

a fluid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the periphery thereof, .a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the side of the element at equally spaced intervals;

a first radiation-sensitive cell mounted within the element;

means for directing observed radiation into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a second radiation-sensitive cell mounted Within the element;

a synchronizing source of radiation positioned externally of the element and being directed toward the second radiation-sensitive cell; and

means for directing a fluid medium through the housing tangentially of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed and standard radiation traveling from their sources to the first radiation-sensitive cell at different times to permit the observed ra-diation and standard radiation to impinge alternately upon the first radiation-sensitive cell to generate a signal indicative of the difference between the a-mounts of the observed radiation and standard radiation irnpinging on the first cell 4and for causing one of the apertures in the element to cross the path of the radiation from the synchronizing source of radiation to the second cell simultaneously with the impingement of radiation from one of the other sources of radiation on the first cell to generate a synchronizing signal.

10. A radiation-sensing device, which comprises:

a housing;

a fluid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the periphery thereof, a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the side of the element at equally spaced intervals;

a first radiation-sensitive cell mounted within the element;

means for directing observed radiation into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

5 a second radiation-sensitive cell mounted within the element;

-a synchronizing source of radiation positioned externally of the element and being directed toward the second radiation-sensitive cell;

means for directing a fluid Imedium through the housing tangentially of the element -against the turbine blades for causing the apertures in the element to cross the paths of the observed and standard radiation traveling from their sources to the first radiationsensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the rst radiation-sensitive cell to generate a signal indicative of the difference between the amounts of the observed radiation and standard radiation impinging on the first cell and for causing one of the apertures in the element to cross the path of the radiation from the synchronizing source of radiation to the second cell simultaneously with the impingement of radiation from `one of the other sources of radiation on the first cell to generate a synchronizing signal; and

means for dernodulating the signals produced by the cells -as a result of the radiation impinging on the cells to produce a signal indicative of the magnitude and direction of any variation between the amounts of the observed and standard radiations striking the first cell.

11. A radiation-sensing device, which comprises:

a housing;

a shaft in the housing;

a fiuid-driven, cylindrical element having an axial bore extending therethrough and a counterbore on each end of the bore, the element having a plurality of turbine blades formed on the periphery thereof symmet-rical with respect to a rounded intersection between one end and the side of the cylindrical element;

bearings mounted in the counterbores in the ends of the cylindrical element for supporting the element rotatably on the shaft in the housing which extends through the axial bore in the element;

a first radiation-sensitive cell mounted within the element on one side of the shaft;

means for direc-ting observed radiation into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect l to the path of the observed radiation toward the cell;

a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the side of the element at equally spaced intervals;

a second radiation-sensitive cell mounted within the element on the opposite side of the shaft;

Ia synchronizing source of radiation positioned externally of the element and being directed toward the second radiation-sensitive cell, thel path of the synchronizing radiation intersecting the side of the element being spaced around the periphery of the cylindrical element an arcuate distance from the intersection of the observed radiation with the path of travel of the apertured portion of the element equivalent to a multiple of the length of the apertures; and

Y means for directing a Afiuid medium through the housing tangentially of the intersecting portion ofthe element against the turbine blades for causing the apertures in the element to cross the paths of the observed radiation and the standard radiation traveling from their sources to the rst radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the rst radiation-sensitive cell to generate a signal indicative of the `difference between the observed radiation and standard radiation, and causing one of the apertures in the element to cross the path of the radiation from the synchronizing source to the second cell simultaneously with the impingement of the radiation from one of the other sources of radiation on the first cell to generate a synchronizing signal.

12. A radiation-sensing device, which comprises:

a housing;

a shaft in the housing;

a fluid-driven, cylindrical element having an axial bore extending therethrough and a counterbore on each end of the bore, the element having a plurality of turbine blades formed on the periphery thereof symmetrical with respect to a rounded intersection between one end and the side of the cylinder;

bearings mounted in the counterbores in the ends of the cylindrical element for supporting the element rotatably on the shaft in the housing which extends through the axial bore in the element;

a rst radiation-sensitive cell mounted within the element on one side ofthe shaft;

means for directing observed radiation Ainto the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a series of circumferential apertures of a predetermined size formed in the side of the element at equally spaced intervals, the length of the apertures and the spacing between successive apertures being substantially equivalent to each other and to the distance between the points the paths of the observed radiation and the standard radiation intersect the path of travel of the apertures in the cylindrical element;

a second radiation-sensitive cell mounted within the element on the opposite side ofthe shaft;

a synchronizing source of radiation positioned externally of the element and being directed toward the second radiation-sensitive cell, the path of the synchronizing radiation intersecting the side of the element being spaced around the periphery of the cylindrical element an arcuate distance from the intersection of the observed radiation with the path of travel of the apertured portion of the element equivalent to a multiple of the length of the apertures; and

means for directing a fluid medium through the housing tangentially of the intersecting portion of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed radiation and the standard radiation traveling from their sources to the rst radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternatively upon the rst radiation-sensitive cell to generate a signal indicative of the difference between the observed radiation and standard radiation, and causing one of the apertures in the element to cross the path of the radiation from the synchronizing source to the second cell simultaneously with the impingement of the radiation from one of the other sources of radiation on the first cell to generate a synchronizing signal.

13. A radiation-sensing device, which comprises:

a housing;

a shaft in the housing;

a fluid-driven, cylindrical element having an axial bore extending therethrough and a counterbore on each end of the bore, the element having a plurality of turbine blades formed on the periphery thereof symmetrical `with respect to a round intersection between one end and the side of the cylinder;

bearings mounted in the counterbores in the ends of the cylindrical element for supporting the element rotatably on the shaft in the housing which extends through the axial bore in the element;

a rst radiation-sensitive cell mounted within the element on one side of the shaft;

means for directing observed radiation into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the side of the element at equally spaced intervals, the length of the apertures and the spacing between successive apertures being subtsantially equivalent to each other and to the separation of the points that the paths of the observed radiation and the standard radiation toward the first cell intersects the path of travel of the apertures in the cylindrical element;

a second radiation-sensitive cell mounted within the element on the opposite side of the shaft;

a synchronizing source of radiation positioned externally of the element and being directed toward the second radiation-sensitive cell, the path of the synchronizing radiation intersecting the side of the element being spaced around the periphery of the cylindrical element an arcuate distance from the intersection of the observed radiation with the path of travel of the apertured portion of the element equivalent to a multiple of the length of the apertures;

means for directing a fluid medium through the housing tangentially of the intersecting portion of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed radiation and the standard radiation traveling from their sources to the rst radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the first radiation-sensitive cell to generate a signal indicative of the difference between the observed radiation and standard radiation, and causing one of the apertures in the element to cross the path of the radiation from the synchronizing Source to the second cell simultaneously with the impingement of the radiation from one of the other sources of radiation ondthe first cell to generate a synchronizing signal; an

means for demodulating the signals produced by the cells as a result of the radiation impinging on the cells to produce a signal indicative of the magnitude and direction of any variation between the observed radiation and the standard radiation.

14. A system for controlling the temperature of a workpiece, which comprises:

a heat-sensing device including a housing;

a fluid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades fon-med on the periphery thereof, a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the element at equally spaced intervals;

a first radiation-sensitive cell mounted within the element;

means for directin-g observed radiation being emitted by a heated workpiece into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a second radiation-sensitive cell mounted within the element;

a synchronizing source of 'radiation positioned externally of the element and being directed1 toward the second radiation-sensitive cell;

means for directing fluid through the housing tangentially of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed and standard radiations traveling from their sources to the rst radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the rst radiation-sensitive cell to generate a signal indicative or" the difference between the observed radiation and the standard radiation, and causing one of the apertures in the element to cross the path of the radiation from the synchronizing source to the second cell simultaneously with the impingment ofrradiation from one of the other sources of radiation on the first cell to generate a synchronizing signal;

a resistance-heating circuit including a pair of contacts engaging opposite sides of the workpiece to be heated;

means for supplying current to the resistance-heating circuit;

means for amplifying the signals produced by the radiation-sensitive cells;

means for demodulating the amplified signals produced by the radiation-sensitive cells to produce an error signal indicative of the magnitude and directionv of any variation between the observed radiation and the standard radiation; and

a phase shifter responsive to the demodulated signal -for controlling the current supplied to the resistanceheating circuit to control the temperature of the workpiece.

- 15. The system for controlling the temperature of a workpiece detined in claim 14 wherein the phase shifter comprises:

atransformer having a'primary winding and a centertapped secondary winding;

a source of alternating voltage connected to said primary winding;

a complementary pair of transistors, each of the transistors having threefelectrodes including an emitter, a collector and a base, the emitters of the transistors being connected together electrically at avcommon point; t

a pair of diodes, each of the diodes having two electrodes, one of the electrodes of one of the diodes being connected to the collector of each of the transistors, the other electrodes of the diodes being connected electrically together at a second common point so that each of the diodes are connected in series with the collector and emitter of the associated transistor;

a capacitor connected between one end of said secondary winding and one of said lcommon points;

the other end of said secondary winding bein-g connected to the other of said common points;

the diodes being mutually oppositely poled to allow current ow through alternate collectorsv of the transistors during alternate positive and negative half cycles of the alternating current to charge and discharge the capacitor; and

means for applying the demodulated error signal to the bases of thetransistors, any variation of current flow through the transistors being a function of the deworkpiece, which comprises:

a heat-sensing device including a housing;

a Huid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the periphery thereof, a series of circumiferential, radiation-transmitting apertures of a predetermined size formed in the element at equally spaced intervals;

a rst radiation-sensitive cell mounted within the eletment;

means for directing observed radiation being emitted by a heated workpiece into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housling externally of the element, the radiation therefrom being directed toward the radiation-sensitive cell ina path oriented angularly of the element with Irespect to the path of the observed radiation toward the cell;

a second radiation-sensitive cell mounted within the element;

a synchronzin-g source of radiation lpositioned externally of the element and being directed toward the second radiation-sensitive cell;

means for directing luid through the housing tangentially of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed and standard radiations traveling from their sources to the irst radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the rst radiation-sensitive cell to generate a signalv indicative of the difference between the observed radiation and the standard radiation, and causing one of the apertures in the element to cross the path of the radiation from the synchronizing source i tto the second cell simultaneously with the impingement of radiation from one of the other sources of radiation on the rst cell to vgenerate a synchronizing signal;

a resistance-heating circuit including a pair of contacts engaging opposite sides of the workpiece to be heated;

means for. supplying current to the resistance-heated circuit including a silicori-controlled-rectier unit, the silicon-controlled-rectifier unit including two siliconcontrolled rectiers;

a pulser unit including a unijunction transistor for supplying trigger pulses for controlling the silicon-controlled-rectifier unit;

i means for supply anode voltages to the silicon-controlled rectiliers; means for amplifying the signals produced by the radiation-sensitive cells; means for demodulating the amplified signals produced by the radiation-sensitive cells to produce a signal indicative of the magnitude and direction of any variation between the observed radiation and standard radiation; and a phase shifter responsive tothe demodulated signal for controlling the phase angle of the trigger pulses relative t-o the anode voltages impressed on the silicon-controlled rectiers to control the current supplied to the resistance-heating circuit by the siliconcontroller rectifier unit to control the temperature of the workpiece.

17. A system for controlling the temperature of a workpiece, which comprises:

a heat-sensing device including a housing;

a iiuid-driven element mounted rotatably in the housing, the element having a plurality of turbine blades formed on the periphery thereof, a series of circumferential, radiation-transmitting apertures of a predetermined size formed in the element at equally spaced intervals;

a first radiation-sensitive cell mounted within the houslng means for directing observed radiation being emitted by a heated workpiece into the interior of a housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing, the radiation therefrom being directed toward the radiation-sensitive cell in a path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a second radiation-sensitive cell mounted within the housing;

a synchronizing source of radiation being directed toward the second radiation-sensitive cell;

means for directing fluid through the housing tangentially of the element against the turbine blades for causing the apertures in the element to cross the paths of the observed and standard radiation traveling from their sources to the first radiation-sensitive cell at different times to permit the observed radiation and standard radiation to impinge alternately upon the first radiation-sensitive cell to generate a signal indicative of the difference between the observed radiation and the standard radiation, and causing one of the apertures in the element to cross the path of the radiation from the synchronizing source to the second cell simultaneously with the impingement of radiation from one of the other sources of radiation on the first cell to generate a synchronizing signal;

a resistance-heating circuit including a pair of contacts engaging opposite sides of the workpiece to be heated;

`means for supplying current to the resistance-heating circuit;

means for amplifying the signals produced by the radiation-sensitive cells;

means for demodutlating the amplified signals produced by the radiation-sensitive cells to produce a signal indicative of the magnitude and direction of any variation between the observed radiation and standard radiation; and

a phase shifter responsive to the demodulated signal for controlling the current supplied to the resistanceheating circuit to control the temperature of the workpiece.

18. A current-Variable resistance circuit which comprises:

a complementary pair of semiconductive devices of oppositely conductive types, each of the semiconductive devices having at least three electrodes including a first electrode, a second electrode and a control electrode, said first electrode of each of the semilconductive devices being connected electrically to a first common point;

means for supplying a common D.C. control current to the control electrodes, said current passing from the control electrode of .one device through the commonly connected first electrodes of the devices and through the control electrode of the other device;

a pair of diodes, each of the diodes being connected between the second electrode of an associated one of the semiconductive devices and to a second common point;

means for impressing an A.C. voltage across the two common points, the diodes being mutually oppositely 16 poled to permit the alternating current to liow between the two common points through alternate devices during alternate half cycles in the same direction as the common control current flowing through the second electrode of the then conducting device; and

means for varying the common control current to vary the effective resistance between the co-mmon points.

19. A phase shifter which comprises:

a complementary pair of semiconductive devices of oppositely conductive types, each of the semiconductive devices having at least three electrodes including ,a fi'rst electrode, a second electrode and a control electrode, said first electrode of each of the semiconductive devices being connected electrically to a first common point;

a pair of diodes, each of the diodes being connected between the second electrode of an associated one of the semiconductive devices and a second common point;

a reactive component, one end of the reactive cornponent being connected to one of said common points;

a transformer having a primary winding and a centertapped secondary winding, the opposite ends of the center-tapped secondary winding being connected between the other end of the reactive component and the other of said common points;

fa source of alternating voltage connected to said primary winding;

the diodes being mutually oppositely poled to permit an Aalternating current to flow between the two common points through alternate devices during alternate half cycles in the same direction as the common control current flowing through the first electrode -of the then conducting device; and

means for supplying a common variable D.C. control current to the control electrodes of the devices, said control current passing from the control electrode of one device through the commonly connected rst electrodes of the devices and through the control electrode of the other device so that any variation in the common control current will vary the effective resistance between the common points for varying the phase angle of an output signal between the center tap of said secondary 4winding and the common point to which the reactive component is connected.

20. A phase shifter according to claim 19 wherein the reactive component comprises:

a capacitor.

' 21. A system for controlling the temperature of a workpiece,

means for heating a workpiece; means for detecting radiant energy; a standard source of radiant energy;

means for alternately exposing the means for detect- `v ing radiant energy to radiant energy from the workpiece and from the standard source to generate a signal;

means for generating 'a synchronizing signal;

means for demodulating the signals to generate an error signal indicative of the magnitude and direction of any variations in the temperature of the workpiece and the temperature of the standard source of radiation;

a transformer having a primary winding and a centertapped secondary winding; l

a source of alternating voltage connected to said primary winding;

a complementary pair of transistors, each of the transistors having three electrodes including an emitter, a collector and a base, the emitters of the transistors being connected together electrically at a common point;

a pair of diodes, each of the diodes having two electrodes, one of the electrodes of one of the diodes being connected to the collector of each of the transistors, the other electrodes of the diodes being connected electrically together at a second common point so that each of the diodes are connected in series with the collector and emitter of the associated transistor;

a capacitor connected between one end of said secondary Winding and one of said common points;

the -other end of said secondary winding being connected to the other of said common points;

the diodes being mutually oppositely poled to allow -current flow through alternate collectors of the transistors during alternate positive Iand negative half cycles of the alternating current to charge and discharge the capacitor;

means for applying the demodulated error signal to the bases of the transistors, any variation of current flow through the transistors being a function of the demodulated signal applied to the bases and in elfect varying the conductance of the transistors, thereby varying the phase angle of the output voltage between the center tap of said secondary Winding and said common point to which the capacitor is connected; and

means responsive to the phase angle of the output voltage for controlling the means for heating the Workpiece.

22. A radiation sensing device, which comprises:

a housing;

a radiation chopping element mounted rotatably in the housing, the element having la series of circumferen- 18 tial radiation-transmitting apertures of a predetermined size formed in the side of the element at equally spaced intervals;

a rst radiation-sensitive cell mounted Within the houslng? means for directing observed radiation into the interior of the housing toward the radiation-sensitive cell;

a standard source of radiation positioned in the housing, the radiation therefrom being directed toward the radiation-sensitive cell in the path oriented angularly of the element with respect to the path of the observed radiation toward the cell;

a second radiation-sensitive cell mounted Within the housing;

a synchronizing source yof radiation being directed toward the second radiation-sensitive cell; and

means for rotating the radiation chopping element.

References Cited UNITED STATES PATENTS 2,547,212 4/1951 Jamison et al. 88-14 X 2,783,384 2/1957 Bright et al. 307-885 X 2,870,343 1/1959 Golay 88-14 X 2,890,418 6/1959 Zawels 307-88-5 X 2,978,589 4/1961 Howell 88-14 X 3,007,103 10/1961 Ehret 307-885 X 3,163,700 12/1964 Williamson 88-14 X 3,183,366 5/1965 Brode 307-885 X RICHARD M. WOOD, Primary Examiner.

B. A. STEIN, Assistant Examiner. 

1. A RADIATION CHOPPER WHICH COMPRISES: MEANS FOR DIRECTING A BEAM OF RADIATION ALONG A PREDETERMINED PATH; A UNITARY ROTATABLE ELEMENT HAVING A PLURALITY OF TURBINE BLADES FORMED THEREON AND PROVIDED WITH AT LEAST ONE RADIATION-TRANSMITTING APERTURE, THE APERTURE BEING ARRANGED FOR MOVEMENT PERIODICALLY ACROSS THE BEAM OF RADIATION DURING ROTATION OF THE ELEMENT; AND MEANS FOR DIRECTING A FLUID MEDIUM AGAINST THE TURBINE BLADES TO ROTATE THE ELEMENT TO CAUSE PERIODIC TRANS- 